Truth About Switching Geysers Off?

Arthur said:
Good points. As an aside, my "trivial" point is in reference to the 'Newtonian loss', ie the different rate of cooling at different temps.

But whatever your standing loss, when you switch on again in the evening/night you still have to make up the heat loss (whatever it is) to get back to 60 deg C.
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Most of what you need to make up is the usage - not the loss which would have already have been made up if the geyser were on all the time.

The trick to having the timer system save electricity is to have the timer reheat the geyser before you use it. It doesn't help to heat the geyser to 60 after you're done at leave it for the whole day. That will have a relatively small difference to running the geyser constantly, but if you use the geyser shortly after it's been on and allow it to cool, it can make a large difference.
Maybe that's why some people haven't seen benefits and others have. Maybe some people are switching off a hot geyser instead of switching it off before using it.
 
With anything that takes 140+ posts , I have to assume the jury is still out.
 
me_ said:
Most of what you need to make up is the usage - not the loss which would have already have been made up if the geyser were on all the time.

The trick to having the timer system save electricity is to have the timer reheat the geyser before you use it. It doesn't help to heat the geyser to 60 after you're done at leave it for the whole day. That will have a relatively small difference to running the geyser constantly, but if you use the geyser shortly after it's been on and allow it to cool, it can make a large difference.
Maybe that's why some people haven't seen benefits and others have. Maybe some people are switching off a hot geyser instead of switching it off before using it.
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Precisely!

One only gets the optimal saving if one fully understands the hot water usage pattern (or deliberately manipulate the usage pattern to achieve optimal power savings).

Once one is fully aware of how hot water is used, one can then determine when to switch on the geyser to get the geyser back to the set temperature, then witch OFF and allow the hot water to be used up. There is no point in leaving the geyser on and switching off a hot geyser.

Using on-off cycles works for those that have taken the trouble to understand how their systems works. ...... and know how long it takes to warm up a cold geyser and how much hot water is left over in a geyser after everyone has drawn hot water .. This take many measurements to get right....
 
I just don't understand why someone can't take an isolated geyser - measure electricity for a month with it plugged in and then measure electricity for one month with it switched off overnight and then a third month with it switched off during the day. And compare.
 
They have. There are numerous studies done by universities and colleges, for example.

Some are referenced above in this thread.

And they all show that, assuming the same amount of hot water at the same temperature is used, the power savings are negligible.
 
According to the technical director of Kikot:

The standard hysteresis is 7º for domestic water heaters. Once a steady state condition is achieved, the switching intervals when no water is being used, can be several hours.

This means that once your water has reached maximum temperature and switched off, it must cool down by 7º before the geyser is once again switched on by the thermostat. It will then use as much electricity as is required to heat the geyser by 7º, before repeating the cycle. The actual electricity used will depend mainly upon how many litres are stored.
 
bekdik said:
The standard hysteresis is 7º for domestic water heaters. Once a steady state condition is achieved, the switching intervals when no water is being used, can be several hours.
.
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(sorry to resurrect another zombie thread on Geysers - should I turn them off - but was asked a question on our blog and thought I'd better link to here!)

That's the problem with 'experts' :) he's looking at the numbers and not looking at real life...

It doesn't matter what the geyser does -- any engineer or scientist will tell you, provably so, that unless the geyser cools all the way down to ambient, you will save hardly any energy by switching it off.

What they miss out is that if the geyser is OFF they use COLDER water to do the same things... and that DEFINITELY saves you money. When you wash your hands... you don't care if the hot water is 60 degrees or 40 degrees. In fact if it's hotter you end up using more water because its too hot, then you switch on the cold tap to cool if off and run the tap longer etc...
Until it's REALLLY COLD, most people don't realise that it's colder, they just cope with it.

And any scientist or engineer WILL tell you that if your hot water is 40 degrees rather than 60 degress, you WILL save energy...

I know myself that when I use the shower I generally turn on the hot tap, and then once it's warmed up, turn on the cold tap until I can shower without being burned. Basically, if the water is hotter, I just end up with a faster flow of water... If the water was 'barely' hot enough (say 40 degrees), I'd have a lower flowing shower, and spend less on energy.

Sorry it's convoluted. But I'll come back down to it -- it is impossible for you geyser to use MORE energy by being switched off!
Any real savings from switching off will only come from:
A: it cooling ALL the way down (which should take days/a week or so, assuming it's good, but could be quick if there's leaks, bad lagging etc.)
B: Using cooler hot water -- i.e. you wash dishes at 30 degrees, rather than 40 degrees.

That's it...
 
my problem is these damn mixer taps - they put the hot water on the RHS (dumb!) which you tend to use more (easier to put the RHS tap on with right hand) so you end up using hot water for everything when you should be using cold and THAT definitely uses more electricity.
 
I really wish there were some real world tests with geysers

turn on vs turn off for x hours per day.

low temp setting vs high temp setting

even the second is open for dispute - does it save to have a low temp and then not use cold water with it, which means you actually use MORE hot water every time you run the tap but does the lower temp compensate, or is it better to have the geyser hotter and you use less each time (which means less to reheat) every time you use it because you dilute it at the tap / basin / bath / shower?

I don't think you can theorise those real world results. Yes x water takes x to heat, but how is that affected by how hot it was to start off with, how much water you take out the system, and how much cold goes in to refill it?

FYI a smaller geyser gets unusably cold damn fast (like overnight) and even faster if you use water out of it and cold water goes in to refill it.
 
Arthur said:
They have. There are numerous studies done by universities and colleges, for example.
Some are referenced above in this thread.
And they all show that, assuming the same amount of hot water at the same temperature is used, the power savings are negligible.
Click to expand...

PS - and that's exactly the point... and I hope one we can all agree on.

You don't save* by switching off your geyser. You save by using cooler water... switching off a geyser is a way to achieve that.

Its a bit like saying why does my car use up more fuel... scientists have shown that it doesn't matter how you drive, as long as you drive at the same speed and in the same gear there's no difference in efficiency in how you press the accelerator....
In a controlled environment with the same inputs/outputs, you don't save ... but in a real-life environment, you effectively demand LESS from your geyser, when it's off.


* - well, very little saving anyway, unless you're going away for a week or more... or there's a leak (i.e. you're using hot water that you aren't 'using'), or your insulation is crap...
 
richjdavies said:
PS - and that's exactly the point... and I hope one we can all agree on.

You don't save* by switching off your geyser. You save by using cooler water... switching off a geyser is a way to achieve that.

Its a bit like saying why does my car use up more fuel... scientists have shown that it doesn't matter how you drive, as long as you drive at the same speed and in the same gear there's no difference in efficiency in how you press the accelerator....
In a controlled environment with the same inputs/outputs, you don't save ... but in a real-life environment, you effectively demand LESS from your geyser, when it's off.


* - well, very little saving anyway, unless you're going away for a week or more... or there's a leak (i.e. you're using hot water that you aren't 'using'), or your insulation is crap...
Click to expand...

There is a trade off on when to turn it off and keeping it hot enough. If you have the data, you can optimise for it by looking at your usage patterns.

These guys have modeled it mathematically and found that you can reduce total energy usage by 9-16% by switching the geyser off. They also did a survey showing that most people have no idea in how to correctly choose their geysers.
Energy perceptions in South Africa: An analysis ofbehaviour and understanding of electric waterheaters
 
I have spent 45 years controlling geysers with timers, and I know in our family situation we definitely save power and water by NOT leaving the geyser and its thermostat to "control" water temperature by itself.

It is complete lifestyle adjustment that is required, where the behaviour of family members is "manipulated" to get the savings. It has very little to do with the mechanics and the physics of water heating.

Family members need to know that hot water is not freely available and limited in quantity and has to be shared when it is available. THIS is where the biggest savings come from, and you do it by means of a timer, that will only allow the water to be heated when needed.

Now we can argue about what one can do to ensure that the water heating system you have is working optimally.

(1) Older geysers and most geysers installed in houses are not of the highest rating. Even now a plumber will win the tender by quoting the lowest price, and generally Grade D geysers are installed, which are not particularly good when it comes to heat retention. So the issue is about heat loss and the only way to improve this situation is with a geyser blanket. Even if one installs a grade A geyser, added insulation helps to reduce heat loss.
(2) Insulate ALL pipes to and from the geyser as far as can be done, not just 1 meter from the geyser. This further reduces heat loss and it means hot water once heated takes longer to cool down before the thermostat will trigger anyway. It does not matter what the hysteresis temperature is, the geyser will simply not use power when the timer does not deliver power to the geyser.
(3) IF you have to change the geyser, bite the bullet and makes sure the highest grade geyser possible is installed as a replacement, not just any old geyser. this is difficult when home insurance companies are involved in the decision making process, but, you have to take over this process regardless of what they will cover, by agreeing to pay the difference if required. This is also the right time to take that decision to go "green" with an alternative technology such as Solar or Heat Pump or gas, whatever floats your boat.
(4) Find out which hot water taps are the furthest from the geyser, because these taps will result in the loss of the most water while waiting for the hot water to come through. Typically it is the kitchen and the laundry. Seriously consider installing an alternative in line electric heater in that line right below the sink, which will see to it that hot water is instantly available, reducing water wastage and hot water consumption.
(5) Measure, measure and measure some more, to determine what the best temperature setting is for your circumstances. NOONE can tell you what will work for your setup, because everything including the types of taps, pipe runs etc influences the final chosen temperature.
(6) make sure your setup complies with the law on temperature control. Hot water ( temperature measured at the tap) in South Africa is now supposed to be at no colder than 60 degree C, to combat bacteria growth such as Legionnaires disease. BUT this has to be balanced against what is considered safe to protect persons form being inadvertently burnt. The final temperature you set the geyser at is then set to achieve whatever temperature you decide water should be when it comes out of the hot water tap. (55 - 60 degrees is generally considered the compromise between bacteria control and safety).

BUT having said all of this, The hotter the geyser runs, the higher the losses will be BUT the less hot water consumption is, and the trade off is SAFETY. One has to be more cautious to ensure scalding does not happen.

The lower the temperature, the more hot water will be used, meaning the geyser will have to heat up more water, which does push up the heating costs, especially if nothing is done about controlling heat losses.

If one installs a modern temperature control setup, one can then not rely on the thermostat in the geyser at all to control the temperature, allowing for much more control and fine tuning to suit your circumstances.
 
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konfab said:
There is a trade off on when to turn it off and keeping it hot enough. If you have the data, you can optimise for it by looking at your usage patterns.

These guys have modeled it mathematically and found that you can reduce total energy usage by 9-16% by switching the geyser off. They also did a survey showing that most people have no idea in how to correctly choose their geysers.
Energy perceptions in South Africa: An analysis ofbehaviour and understanding of electric waterheaters
Click to expand...

A great reference! Thanks for the link. Seems to fully support everything I have said in my post.
 
konfab said:
There is a trade off on when to turn it off and keeping it hot enough. If you have the data, you can optimise for it by looking at your usage patterns.

These guys have modeled it mathematically and found that you can reduce total energy usage by 9-16% by switching the geyser off. They also did a survey showing that most people have no idea in how to correctly choose their geysers.
Energy perceptions in South Africa: An analysis ofbehaviour and understanding of electric waterheaters
Click to expand...

Those % savings do not tell the whole story. That article specifically states the following:
The standing losses of an EWH in South Africa must meet a minimum specifications outlined in the South African National Standard (SANS)151, which stipulates that the maximum tolerable standing losses for a 150 and 200 litre EWH at 65°C over a 24 hour period is 2.59 and 3.02 kWh respectively
Click to expand...

and:
When switching the EWH off intermittently, it is possible to reduce the standing losses of the EWH, not the amount of energy consumed by usage events.
Click to expand...

So savings can only be achieved on the standing losses portion, which can be a maximum of 2,59 kWh a day for a 150 litre geyser. That is 2,59 units a day, at say R1 a unit (depends on where you live and amount you use, can go up to R2 or R3 a unit) the standing losses on your geyser is a maximum of R77,70 per month. The article claims savings of 20% - 30% on the standing losses, so a R23 saving per month (at 30%).

If you want to save more, you need to use less hot water. That is basically what everybody else is saying above, you need to change your expectations. Take colder showers, shorter showers, only use hot water when necessary, etc...

For me, the R23 a month is not worth the cost of a timer, nor the inconvenience of planning my life around hot water usage.
 
richjdavies said:
What they miss out is that if the geyser is OFF they use COLDER water to do the same things... and that DEFINITELY saves you money. When you wash your hands... you don't care if the hot water is 60 degrees or 40 degrees. In fact if it's hotter you end up using more water because its too hot, then you switch on the cold tap to cool if off and run the tap longer etc...
Until it's REALLLY COLD, most people don't realise that it's colder, they just cope with it.

And any scientist or engineer WILL tell you that if your hot water is 40 degrees rather than 60 degress, you WILL save energy...

I know myself that when I use the shower I generally turn on the hot tap, and then once it's warmed up, turn on the cold tap until I can shower without being burned. Basically, if the water is hotter, I just end up with a faster flow of water... If the water was 'barely' hot enough (say 40 degrees), I'd have a lower flowing shower, and spend less on energy.

Sorry it's convoluted. But I'll come back down to it -- it is impossible for you geyser to use MORE energy by being switched off!
Any real savings from switching off will only come from:
A: it cooling ALL the way down (which should take days/a week or so, assuming it's good, but could be quick if there's leaks, bad lagging etc.)
B: Using cooler hot water -- i.e. you wash dishes at 30 degrees, rather than 40 degrees.

That's it...
Click to expand...
I have always had a shower with approximately the same flow rate regardless of water temperature. If the hot and cold have to be adjusted independently I'll typically use both taps, increasing one and reducing the other to reach the desired temperature. Perhaps that is why I've never saved by turning off the hot water cylinder. I'll also run the hot only for longer if I am trying to do something that requires really hot water, which would then increase my water heating requirements.

The same principle applies to running a bath. Hotter water means less pulled from the cylinder for the required volume and bath temperature.

I have only one rule for water temperature when washing dishes - if I can comfortably put my hands in the water it is too cold.

Zoomzoom said:
my problem is these damn mixer taps - they put the hot water on the RHS (dumb!) which you tend to use more (easier to put the RHS tap on with right hand) so you end up using hot water for everything when you should be using cold and THAT definitely uses more electricity.
Click to expand...
Not one of my mixer taps has the hot on the right, but I also don't find any preference for which side I turn on, going only for the side that will supply the water I require, hot or cold.
 
Zoomzoom said:
my problem is these damn mixer taps - they put the hot water on the RHS (dumb!) which you tend to use more (easier to put the RHS tap on with right hand) so you end up using hot water for everything when you should be using cold and THAT definitely uses more electricity.
Click to expand...

There is no law that governs which side the hot water should be in SA as far as I know.

In the USA it seems hot water should be on the LHS. In the UK it started being on the LHS.

The problem is it should be the same for all taps in a home, if it is LHS then all should be LHS. My home? All over the place. Before I installed mixer taps on the baths, the main BR bathroom had the basin on the RHS and the bath on the LHS. The second bathroom it was the reverse. On the basin it was LHS and the bath was RHS. The shower was LHS. The kitchen was RHS.

Pretty much nothing you can do about it. The mixer taps I installed (Cobra) are all Hot on the LHS. I was obliged due to the pipe layout to change the indicators when the pipes were wrong.
 
Zoomzoom said:
my problem is these damn mixer taps - they put the hot water on the RHS (dumb!) which you tend to use more (easier to put the RHS tap on with right hand) so you end up using hot water for everything when you should be using cold and THAT definitely uses more electricity.
Click to expand...

So swop the pipes...it takes 20 minutes.

Or just use your memory.

I don't know who "they" are though. Sounds like a spastic plumber to me.

Even as a lefty I put my hot water on the left. And when I bought this house one of the taps was inverted and I swopped it around in the first month.

But ultimately you should be washing your hands with warm water...otherwise not bother washing them at all really.
 
daniellgr said:
Pretty much nothing you can do about it. The mixer taps I installed (Cobra) are all Hot on the LHS. I was obliged due to the pipe layout to change the indicators when the pipes were wrong.
Click to expand...


For a bath or shower it might not be possible.

For a basin it should be quite simple.
 
SauRoNZA said:
So swop the pipes...it takes 20 minutes.

Or just use your memory.

I don't know who "they" are though. Sounds like a spastic plumber to me.

Even as a lefty I put my hot water on the left. And when I bought this house one of the taps was inverted and I swopped it around in the first month.

But ultimately you should be washing your hands with warm water...otherwise not bother washing them at all really.
Click to expand...

I presume you are talking about when flexible connections can be used to connect the pipes to the mixer taps?
Not always possible to swop the pipes. Can only then swop the indicator around.
 
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